Most parents can sympathize with the disturbing sight of a toddler, who five minutes earlier had been jumping off the couch, now subdued and staring at a screen, seemingly hypnotized. In the somewhat alarmist Endangered Minds: Why Children Don’t Think—and What We Can Do About It, author Jane Healy even gives the phenomenon a name, the “ ‘zombie’ effect,” and raises the possibility that television might “suppress mental activity by putting viewers in a trance.”

Should parents be worried? Rosin offers this reassuring info:

These findings have been largely discarded by the scientific community, but the myth persists that watching television is the mental equivalent of, as one Web site put it, “staring at a blank wall.” These common metaphors are misleading, argues Heather Kirkorian, who studies media and attention at the University of Wisconsin at Madison. A more accurate point of comparison for a TV viewer’s physiological state would be that of someone deep in a book, says Kirkorian, because during both activities we are still, undistracted, and mentally active...

By now, “there is universal agreement that by at least age 2 and a half, children are very cognitively active when they are watching TV,” says Dan Anderson, a children’s-media expert at the University of Massachusetts at Amherst.